Suspended structures

These are a very particular type of structures that are based on the use of cables (usually made of steel) that support all the weight. They are mainly used in the construction of bridges since this type of structure allows to cover great distances with low material consumption.

(Steel cable)

Two types of bridges must be distinguished:

• Suspension bridges: are those in which some cables, usually two, are placed on towers and then anchored at their ends. Secondary cables called suspenders hang from the main cables and are fixed to the deck, standing the weight of the road and of the vehicles that circulate on it:

(Parts of a suspension bridge, original image)

The following pictures show several parts of a real suspension bridge:

The construction process of a suspension bridge is as follows:

1. Build the foundations.
2. Raise the towers.
3. Lay the cables and fix them to the anchorages.
4. Hang the suspenders.
5. Fix the parts of the deck to the suspender cables.

(Original image)

The following video explains how one of the most complicated steps in the construction of these bridges is carried out: laying the cables on the towers.

And below you can see two examples of suspension bridges, the well known Golden Gate of San Francisco (United States) and the Hardanger Bridge, which crosses one of the fjords of Norway (the bridge that appears in the previous video).

• Cable-stayed bridges: are those in which the structure is supported directly by steel cables that are anchored at one end to the towers and at the opposite to the deck:

(Parts of a cable-stayed bridge, original image)

As you can see in the images a great variety of cable-stayed bridge exist:

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Both suspension bridges and cable-stayed bridges are very often used to connect two areas that are separated by a river or a sea. In these cases, it is necessary to fix the towers on a ground that is completely underwater. Therefore, it is necessary to dry an area, building a drawer from which water can be extracted:

You must also know that, although the most common application of suspended structures is the construction of bridges, there are also other types of buildings that make use of cables as a supporting element. An example is the roof of the Montreal Olympic Stadium, which hangs from a leaning tower as you can see in the image:

Or the stairs in the image below, whose steps hang directly from a series of steel cables attached to the upper floor of the building:

(Suspended staircase in the House of Music, Budapest, original image)

*Exercise 5.

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